The invention addresses a method of detecting surface contamination by an analyte by wiping the analyte off the surface with the aid of a wiping surface, eluting the analyte from said wiping surface and detecting the analyte in the eluate in an immunological detection reaction. Moreover, the invention also addresses a corresponding analysis element.
In addition to the detection of analytes in sample liquids, such as blood, urine, saliva, the detection of analytes on solid surfaces such as furniture and baggage has gained increasingly more importance in criminal sciences. Especially in the fight against drugs, it is desirable to have a simple and rapid way of detecting even very small amounts of drugs on objects. With an increased degree of sensitivity of the detection, it is, of course, possible to detect even smaller amounts of analyte on a given contaminated surface.
In order to test for analytes, especially drugs, on any desired surface, various special detection techniques are known where the analyte is first collected by wiping the surface and then immunologically detecting after eluting, the analyte from the surface used for the wiping. In case of the xe2x80x9cIllicit Substance Detectorxe2x80x9d manufactured by Westinghouse, Baltimore, USA (Security Management, Vol. 37/8, pages 12-15, 1993), the surface to be examined is wiped with a napped plastic material, and the drug is detected via a method with three reagent solutions that are integrated in a disposable card (DE-A-4341862). The test result is evaluated with an optical reader. The principle of this immunological detection is based on the inhibition of a latex agglutination reaction by the drug to be detected. The lower detection limit is indicated in micrograms. Despite the high detection limit, it is a disadvantage that the detection reaction must be started by mechanically squeezing the three liquid reservoirs. Moreover, the result can only be evaluated with an optical reader and not with the bare eye.
Roche Diagnostics is the manufacturer of a test kit to detect cocaine from urine samples according to the same complex immunological detection principle. The sensitivity of this detection ranges around 0.2 xcexcg/ml.
The xe2x80x9cAccupress Kitxe2x80x9d manufactured by Thermetics, Woburn, USA (Security Management, Vol. 37/8, pages 12-15, 1993) comprises a reagent carrier having a special coating and three vessels containing reagent solutions. In this test, the surface to be examined is wiped with a cotton swab; and the swab is then washed with buffer. In addition to the comparable insensitive detection limit of not below 1 xcexcg, the handling of these three different reagent solutions is also inconvenient and is a source of errors.
It was, hence, an object of the invention to provide a more sensitive method of detecting analyte contamination of surfaces, especially traces of drugs, which can be carried out in a simple manner and without technical support means. Especially the detection limit for the analyte should be significantly below 1 xcexcg, absolutely, and if possible below 100 ng.
This object is accomplished with a method and analysis element as characterized in the claims.
Subject matter of the invention is a method of detecting surface contamination by an analyte by wiping the analyte off the surface with a wiping surface, eluting said analyte from the wiping surface and detecting the analyte in the eluate in an immunological assay, is characterized in that
a) the surface to be tested for the analyte is wiped with the wiping surface,
b) the wiping surface is brought into contact with the planar surface of a capillary, chromatographic test strip which, at its one end, has an application zone for applying an eluant liquid and, at its other end, a target zone, whereby contact is made in an area between these two zones,
c) eluant liquid is applied onto the application zone, said liquid moving toward the target zone passing the contact site with the wiping surface as a consequence of capillary forces, whereby analyte is absorbed by the eluant, and
d) in the target zone, the analyte is measured in an immunological binding reaction.
The test strip for the method in accordance with the invention can be made of one single chromatographic strip-like material, or preferably several capillary surfaces made of the same or different materials and disposed on a base layer are essentially arranged next to one another. Said surfaces are in a fluid contact to each other so as to form a transport path along which a liquid driven by capillary forces flows from the eluant application zone toward the target zone.
Possible chromatographic materials are all liquid-absorbent, porous, or capillary active materials, such as cellulose or its derivatives, glass fiber, and fleeces, and fabrics made of synthetic or natural materials.